Polyester polymers having various compositions are present as described below and employed widely in various industrial fields.
A polyethylene terephthalate (hereinafter abbreviated as PET) is excellent in terms of mechanical properties, chemical properties, transparency, heat resistance and gas barrier performance, and can be used in various products such as fibers for clothing and industrial materials, films or sheets for packages or magnetic tapes, molded articles such as bottles and engineering plastics.
A PET is produced industrially by an esterification or a transesterification of terephthalic acid or dimethyl terephthalate with ethylene glycol to form bis(2-hydroxyethyl)terephthalate followed by a polycondensation at a high temperature under vacuum using a catalyst.
A polyethylene naphthalate (PEN) is excellent in terms of heat resistance, impact resistance, transparency, gas barrier performance, UV-shielding ability and chemical resistance, and thus is used in bottles, films, sheets and fibers for industrial materials.
A polyethylene naphthalate is produced industrially by an esterification or a transesterification of naphthalenedicarboxylic acid or dimethyl naphthalenedicarboxylate with ethylene glycol to form a low molecular weight oligomer followed by a polycondensation at a high temperature under vacuum using a catalyst.
A polybutylene terephthalate (PBT) is excellent in terms of moldability, heat resistance, mechanical properties, chemical resistance and the like, and thus is employed widely as a material for a molded article such as automobile parts and electric or electronic parts.
A PBT is produced industrially by an esterification or a transesterification of terephthalic acid or dimethyl terephthalate with 1,4-butanediol to form a low molecular weight oligomer followed by a polycondensation at a high temperature under vacuum using a catalyst.
A polypropylene terephthalate is excellent in terms of heat resistance, impact resistance, transparency, chemical resistance, weather resistance, electric properties, pliability and the like, and thus is employed widely in fibers, films, automobile parts, electric or electronic parts and the like.
A polypropylene terephthalate is produced industrially by an esterification or a transesterification of terephthalic acid or dimethyl terephthalate with propanediol to form a low molecular weight oligomer followed by a polycondensation at a high temperature under vacuum using a catalyst.
A cyclohexanedimethanol-modified polyethylene terephthalate (hereinafter referred to as CHDM-modified PET) is excellent in terms of impact resistance, transparency, gas barrier performance, chemical resistance, recycling applicability and the like, and thus is employed in various molded articles such as sheets.
A CHDM-modified PET is produced by an esterification of terephthalic acid with ethylene glycol and cyclohexanedimethanol, or a transesterification of dimethyl terephthalate with ethylene glycol and cyclohexanedimethanol to form a low molecular weight oligomer followed by a polycondensation at a high temperature under vacuum using a catalyst.
A polyester fiber employing a polyester described above, especially a PET or a PEN, is an organic fiber which is well-balanced between the physical properties and the cost, and used widely and in a large amount as a filament or a staple not only for clothing but also for various interior articles as well as industrial materials such as padding stuffs or unwoven fabrics.
As a polyester polymerization catalyst employed in a polycondensation to form a polyester as described above, i.e., a polycondensation catalyst, antimony trioxide is employed widely. While antimony trioxide is low-priced catalyst having an excellent catalytic activity, it undergoes the precipitation of a metal antimony upon a polycondensation, which leads to a problem of graying or foreign body formation in a resultant polyester. Under such circumstance, an antimony-free polyester is desired.
In a polyester for a film, the precipitation of metal antimony results in a foreign body in the polyester, which may lead not only to a dirt on a die upon an extrusion but also to a defect on the film surface. Also when used as a starting material for a molded hollow article, it allows a polyester to be crystallized rapidly, resulting in an extreme difficulty in obtaining a satisfactorily transparent molded hollow article.
A foreign body in a polyester then serves as a foreign body in a fiber which may leads to a reduction in the strength and a dirt on a die upon a spinning. Mainly in view of an operation in a process for a polyester fiber, a polyester polymerization catalyst causing no foreign body is desired.
An attempt has been made to use antimony trioxide as a polycondensation catalyst while suppressing the graying of a PET or a foreign body formation. For example in JP 266652, an antimony trioxide is used as a polycondensation catalyst together with a compound of bismuth and selenium to suppress the formation of a black foreign body in a PET. Also in JP-A-9-291141, a use of a sodium and iron oxide-containing antimony trioxide as a polycondensation catalyst is purported to suppress the precipitation of metal antimony. However, such polycondensation catalyst can not accomplish a reduction in the total amount of antimony contained.
In a use where a transparency is required such as a use in a PET bottle, the problem associated with an antimony catalyst is attempted to be solved for example by improving the transparency by specifying the ratio of the amounts of an antimony compound and a phosphorus compound as described in JP-A-6-279579. However, a molded hollow article obtained from a polyester produced by the method described above is not satisfactorily transparent.
JP-A-10-36495 also discloses a continuous method for producing a polyester having a high transparency using antimony trioxide, phosphoric acid and a sulfonic acid compound. However, a polyester obtained by this method has a poor themostability and a resultant molded hollow article has a problematically high acetaldehyde content.
As a catalyst providing a polyester having an excellent catalyst activity and a high thermal stability other than an antimony compound, a germanium compound has already been employed practically, but it is problematically expensive and tends to be distilled from a reaction system during a polymerization, resulting in a change in the catalyst concentration in the reaction system, which leads to a difficulty in controlling the polymerization.
Thus a polymerization catalyst other than such antimony or germanium compound is required which has an excellent catalyst activity and can provide a highly thermostable polyester undergoing almost no thermal degradation when melted for a molding.
As a polymerization catalyst having an excellent catalyst activity other than an antimony compound or a germanium compound, a titanium compound such as a tetraalkoxytitanate or a tin compound has already been proposed, but a polyester produced using such compound readily undergoes a thermal degradation when melted for a molding and a problematically discoloration of a polyester occurs.
A polyester fiber produced using a titanium compound such as a tetraalkoxytitanate or a tin compound readily undergoes a thermal degradation when melted for a molding and a problematically discoloration of a polyester occurs.
An attempt to suppress a thermal degradation in a molding process of a polyester produced using a titanium compound as a catalyst is disclosed in JP-A-10-259296 which involves a use of a titanium compound as a catalyst in a polymerization to obtain a polyester followed by an addition of a phosphorus-based compound. Although it is possible to improve the thermal stability of a polyester by adding a stabilizer such as a phosphorus-based compound to inactivate a catalyst, an efficient incorporation of an additive into a polymer once polymerized is accompanied not only with a technical difficulty but also with an increased expenditure, and thus is not employed practically. The use of an additive itself is not preferably since it serves to increase the expenditure.
Another attempt to suppress a thermal degradation upon a molding process of a polyester is a removal of a catalyst from the polyester. A method for removing a catalyst from a polyester is, for example, a contact between a polyester resin and an extraction solvent which is a supercritical fluid in the presence of an acidic substance as disclosed in JP-A-10-251394. However, a method employing such supercritical fluid is not preferable since it involves a technical difficulty as well as an increased expenditure.
An objective of the invention is to provide a polyester polymerization catalyst consisting mainly of components except for antimony compounds or germanium compounds which exhibits an excellent catalyst activity and yields a highly thermally stable polyester whose thermal degradation upon a molding process is suppressed efficiently without any need of an inactivation or a removal of the catalyst, a polyester obtained using said polyester polymerization catalyst, and a method for producing a polyester using said polyester polymerization catalyst.
Another objective of the invention is to provide PET, PBT, PEN, CHDM-modified PET and polypropylene terephthalate obtained using a polyester polymerization catalyst described above as well as a method for producing the same.
Still another objective of the invention is to provide molded articles, films, fibers, fibers for industrial materials, modified fibers and flame retardant fibers.